(289f) Macroscopic Mechanistic Modeling Studies of Self-Initiated High-Temperature Polymerization of Alkyl Acrylates

The importance of macroscopic mechanistic modeling of polymerization reactors, used for conducting high-temperature (> 100 o C) polymerization of alkyl acrylates, is in its ability to improve the process design and final product (acrylic resin) quality. Polymerization of alkyl acrylates conducted at high-temperatures in a 1 liter RC1 Mettler-Toledo polymerization reactor were found to produce low molecular weight, high functional acrylic resins in the absence of any added extraneous initiators. The previous study on macroscopic mechanistic modeling of spontaneous high-temperature polymerization of alkyl acrylates did not identify the mechanism of the spontaneous initiation or accurately predict the kinetics of the initiation. More recently, quantum chemical studies demonstrated that in spontaneous high temperature polymerization of alkyl acrylates, monomer self-initiation is the most likely mechanism of initiation, and the rate constants of self-initiation were calculated using transition state theory. Using the quantum information that self-initiation is a third-order reaction, detailed kinetic modeling of self-initiated polymerization of methyl and n-butyl acrylate was conducted. Significant differences between model predictions and experimental measurements of monomer-conversion and average molecular weight profiles were observed. One of the causes for the poor prediction of the model can be the inadequacy of the detailed kinetic model to accurately describe the occurrence of different species generated from various reactions in the reactor. A suitable alternative was identified to be the tendency modeling approach, which describes the polymerization system much differently from detailed kinetic modeling. This type of modeling has been previously used to understand the kinetics of extraneously-initiated polymerization of styrene and other monomers. In this study, we develop a tendency model to understand the dynamics and predict the overall kinetics of self-initiated high-temperature polymerization of methyl and n-butyl acrylate in 1 liter RC1 Mettler-Toledo polymerization reactor. Rate constants for the initiation, backbiting and chain-transfer reactions are estimated from monomer conversion and number average molecular measurements by minimizing the sum of squared errors.